The present invention relates to methods and apparatuses for injecting a sample to be analyzed into a chromatography system, and particularly, into a liquid chromatography system. Typically, sample injection apparatuses for liquid chromatography systems include syringes having a barrel and a plunger. The sample can be dissolved in a solvent and adsorbed a stationary phase to form a stationary phase coated with the sample of interest. The coated stationary phase can be loaded into the barrel of the syringe, or the barrel can be pre-filled with the uncoated stationary phase, and the sample of interest can be run through the stationary phase in the barrel of the syringe to coat the stationary phase with the sample of interest.
The coated stationary phase is held in place in the barrel of the syringe between two frits. The plunger can be used to contact an upper frit. The sample injection apparatus can be connected to a fluid line of the liquid chromatography system, and chromatography solvent can be delivered through the plunger, through the upper frit, and into the coated stationary phase. The sample can then be eluted from the coated stationary phase out an outlet of the syringe into the liquid chromatography system. Due to the build-up of back pressure in the syringe, the plunger can back out of the syringe, causing inadequate or undesirable sample injection. Some devices have attempted to lock the plunger in place to prevent the plunger from backing out of the syringe.
Such locking devices have included a series of depressions or apertures along the plunger. A fastener, such as a screw, can be positioned in engagement with a depression or aperture in the plunger to lock the position of the plunger relative to the barrel. In this way, such conventional systems can be cumbersome. Other similar locking devices can include teeth or protrusions that engage depressions or apertures in the plunger, but similar problems arise.